Question

What are some differences between observational studies and experiments, and what issues may arise during data collection or interpretation?

Answer 1

`What are some differences between observational studies and experiments`
this should help answer the first part
http://www.public.iastate.edu/~dnett/S401/nexpvsobs.pdf

Answer 2

I'm not 100% sure about the second part

`what issues may arise during data collection or interpretation?`

I'm assuming they want you to respond and talk about some sort of bias. One way to do that is to not do a random sample and only pick the data points you want. That will skew the data.